High water level blamed for Vale's dam collapse in Brazil

According to experts, the catastrophic failure of Vale's mining waste dam was caused by high water level.

In January 2019, the 86-meter high dam located in the state of Minas Gerais, collapsed triggering mudslides and floods and resulting in 270 casualties. The incident that also caused significant infrastructure damage, was not anticipated as no earthquakes or explosions that could justify a potential loss of integrity had occurred in the area and there were no signs of instability.

The dam was managed by Vale, a multinational company engaged in mining. The incident affected the firm's credibility and, still, its share price is 5% lower than before the disaster.

The failure is under criminal investigation both in Brazil and Germany, where the safety inspector of the dam (TÜV SÜD) is based. 

A report, recently issued by a panel of experts, points out that the failure occurred due to drainage problems of the dam that led to the increase of pore water pressure resulting in soil's liquefaction and loss of stability. The report's purpose was to derive the failure mechanism that resulted in the failure, not to blame a particular organization about the incident.

The dam was designed and constructed using the upstream method, the most economical technique known in which mining waste is gradually stored and forms the dam's wall. According to the report, the drainage system was deficient from the beginning of the dam's operation.

Moreover, the structure was established at a steep slope and became more vulnerable through the decades as more layers of waste were stored. The last layer was built in 2013. Finally, the tailings that were included in the dam consisted of iron ore, a fact that made the construction more brittle, resulting in a sudden and rapid failure (the dam collapsed in less than 10 seconds). The dam's deficient conditions were exacerbated when high precipitation struck the area in January 2019.

According to Peter Robertson, the panel's expert who is also a former Professor and currently a geotechnical consultant, claimed that Vale was aware of the high water level problem that existed. “It’s fair to say they were aware of the high water level and they were taking actions to lower it and the water levels were slowly going down,” Robertson, stated.